It is often desired to coat both sides of a web simultaneously, and to meter the applied coating with blades. Dual blade coaters have been known in the art for many years. An example of one such coater is shown in Quint, U.S. Pat. No. 3,575,134 issued Apr. 13, 1971, and the divisional patent to the same inventor, U.S. Pat. No. 3,889,018 issued June 10, 1975. Quint employs relatively thick elastomeric blades in a range of 1/4" to 1/2" with flat beveled working surfaces which are at least in partially flush engagement with the opposite sides of the web. In Quint, the blades are adjusted about pivot axes which are remote from the blade-engaging surfaces, and thus Quint could not use thin steel blades. He stated that thin steel blades having a thickness of 0.014" to 0.030" would result in the tearing of the paper web and represented that as a practical matter it would be impossible to align them with the web surface so that they would accurately oppose each other.
A more recent patent disclosing apparatus for coating both sides of a web is Zitzow, U.S. Pat. No. 4,063,531 issued Dec. 20, 1977. The problem of precise control of tip alignment in Zitzow is eliminated by causing the opposed blades to be pressed together at the web over a relatively wide transverse region such that the arc of curvature of the blades becomes tangient to the surface of the web against which they are pressed. Again, as in Quint, the blades are mounted for pivotal movement about an axis remote from the contact region, and the coating apparatus is restricted to one in which the blades are adjusted to form equal angles to the web.
In the prior patent of Zink, U.S. Pat. No. 3,882,817 issued May 13, 1975, assigned to the same assignee as this invention, it is suggested that a double sided coater could be made in which the blades are mounted so that they are pivoted about a common axis which includes the apex or tips of the blades, and it was also suggested that they could be mounted for independent movement such as through a 15.degree. angle, for example. No structure was disclosed by means of which the suggested independent angular adjustment of the opposite blades could be achieved. A dip or immersion-type coater was diagrammatically disclosed, and no arrangement was suggested by means of which the coating dwell on either side of the web could be independently controlled.
A single blade coater in which a blade was mounted for pivotal movement about an axis which included the contact region or tip of the blade against the web was shown in Coghill, U.S. Pat. No. 3,187,718 issued June 8, 1965 and assigned to the same assignee as this invention.